linux-kernel - Re: [Intel-gfx] [PATCH RESEND] drm/i915: Fix pipe/transcoder enum mismatches

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Message-ID: <CADMs+9aVfOx3WegtxqmyHF3MxANNeC8Ot3dkNN8uQhYLi5Y_Fg@mail.gmail.com>
Date:   Thu, 13 Jul 2017 09:23:11 -0700
From:   Stéphane Marchesin <marcheu@...omium.org>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Matthias Kaehlcke <mka@...omium.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        intel-gfx <intel-gfx@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michael Davidson <md@...gle.com>,
        Grant Grundler <grundler@...omium.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [Intel-gfx] [PATCH RESEND] drm/i915: Fix pipe/transcoder enum mismatches

On Thu, Jul 13, 2017 at 3:13 AM, Ville Syrjälä
<ville.syrjala@...ux.intel.com> wrote:
> On Wed, Jul 12, 2017 at 07:28:14PM -0700, Stéphane Marchesin wrote:
>> On Fri, May 5, 2017 at 10:40 AM, Ville Syrjälä
>> <ville.syrjala@...ux.intel.com> wrote:
>> >
>> > On Fri, May 05, 2017 at 10:26:36AM -0700, Matthias Kaehlcke wrote:
>> > > El Thu, Apr 20, 2017 at 02:56:05PM -0700 Matthias Kaehlcke ha dit:
>> > >
>> > > > In several instances the driver passes an 'enum pipe' value to a
>> > > > function expecting an 'enum transcoder' and viceversa. Since PIPE_x and
>> > > > TRANSCODER_x have the same values this doesn't cause functional
>> > > > problems. Still it is incorrect and causes clang to generate warnings
>> > > > like this:
>> > > >
>> > > > drivers/gpu/drm/i915/intel_display.c:1844:34: warning: implicit
>> > > >   conversion from enumeration type 'enum transcoder' to different
>> > > >   enumeration type 'enum pipe' [-Wenum-conversion]
>> > > >     assert_fdi_rx_enabled(dev_priv, TRANSCODER_A);
>> > > >
>> > > > Change the code to pass values of the type expected by the callee.
>> > > >
>> > > > Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
>> > > > ---
>> > > >  drivers/gpu/drm/i915/intel_display.c | 4 ++--
>> > > >  drivers/gpu/drm/i915/intel_dp.c      | 6 ++++--
>> > > >  drivers/gpu/drm/i915/intel_hdmi.c    | 6 ++++--
>> > > >  drivers/gpu/drm/i915/intel_sdvo.c    | 6 ++++--
>> > > >  4 files changed, 14 insertions(+), 8 deletions(-)
>> > >
>> > > Ping, any comments on this patch?
>> >
>> > I'm not convinced the patch is making things any better really. To
>> > fix this really properly, I think we'd need to introduce a new enum
>> > pch_transcoder and thus avoid the confusion of which type of
>> > transcoder we're talking about. Currently most places expect an
>> > enum pipe when dealing with PCH transcoders, and enum transcoder
>> > when dealing with CPU transcoders. But there are some exceptions
>> > of course.
>>
>>
>> I don't follow -- these functions take an enum transcoder; what's
>> wrong about passing what they expect? It seems like what you are
>> asking for has nothing to do with the warning here...
>
> There's a warning? I don't get any.

Yup, clang generates a warning.

>
> Anyways, I just don't see much point in blindly changing the types
> because it doesn't actually solve the underlying confusion for human
> readers. It might even make it worse, not sure.

The function expects type A, you pass type B, how can that ever be the
right thing to do?

Stéphane


>
> --
> Ville Syrjälä
> Intel OTC